A teenage girl is found murdered in an alley, having been brutally assaulted and raped. Detectives Briscoe and Green later find a connection to an unsolved Brooklyn homicide from five years earlier, featuring a similar victim and modus operandi. The detectives are able to link several unsolved homicides and missing persons reports and believe them all to be the work of a serial killer. After speaking to some of the victims' families, they realize the victims were all abducted or found far from their homes, meaning they likely summoned a taxi. An investigation of the cab company leads them to the apartment of Mark Bruner, whose unsettling demeanor and evasion of the detectives' questions quickly make him a suspect. He is eventually held and charged with two counts of murder, and DNA evidence points to his irrefutable guilt.

Bruner is remanded without bail at arraignment. His attorney, Jessica Sheets, is so disturbed by her client that she refuses to represent him (it is implied that Bruner threatened her). Bruner is subsequently represented by legal aid lawyer Tim Schwimmer, who wants to use the case to further his career (it is his first murder case, having previously dealt mainly in property damage cases). Jack McCoy is willing to take the death penalty off the table for Bruner if he provides specific details about all of the murders he has committed. During plea negotiations, Bruner reveals vaguely how many girls he murdered (around fifteen). However, he refuses to disclose the location of his victims' bodies, having nothing to gain by doing so, as he feels life in prison is no better than receiving the death penalty. After taunting McCoy and attempting to frighten Serena Southerlyn, Bruner reveals that Schwimmer visited the site where the bodies of his victims are stashed. Schwimmer did not want the ADAs to know that he went to this location. At first, McCoy tries to pressure Schwimmer into revealing the location by leaking word of Schwimmer's actions to the press. Schwimmer's office is picketed by families of missing victims and he receives threats by phone. The previously cocky Schwimmer is now shaken and accosts McCoy for the press leak, for which McCoy does not admit responsibility. Arthur Branch tells McCoy and Southerlyn that Schwimmer was "dumber than stupid" for visiting the location of Bruner's victims and putting himself in this situation. Bruner later says that the bodies were "under lock and key;" McCoy argues that this statement means that Schwimmer had to unlock, and then re-lock, the location where the bodies are; therefore he abetted Bruner's crime by helping to hide the bodies. McCoy has Schwimmer arrested.

At Schwimmer's trial, the parents of five missing girls testify that they need to know if their children are amongst Bruner's victims. Schwimmer regrets his earlier actions but refuses to break attorney–client privilege, arguing that despite the benefit to families who want to put their loved ones to rest, he feels the system wouldn't work if he breaks that confidence. During a private conversation outside the courtroom before the verdict, the ADAs tell Schwimmer that "no bar association in the country would consider disbarring" him for revealing the location, to which he replies, "Shame on them." Schwimmer is subsequently found guilty of being an accomplice to murder. The episode ends with McCoy stating his belief that Schwimmer will reveal what he knows after spending a week in Attica, to which Southerlyn replies, "I don't think so. We put the system on trial, we lost." McCoy speaks the last line of the program: "Knock on wood."